1. Technical Field
The present invention relates to a transflective liquid crystal display device in which one dot region includes a reflective display region and a transmissive display region and to an electronic apparatus including the same.
2. Related Art
Transflective liquid crystal display devices having both a reflective mode and a transmissive mode have been generally known as liquid crystal display devices. As the transflective liquid crystal display device, a display device has been suggested in which a liquid crystal layer is interposed between an upper substrate and a lower substrate, and a reflective film obtained by forming light-transmissive windows in a metal film made of, for example, Al is provided on an inner surface of the lower substrate to function as a transflective plate. In this case, in the reflective mode, external light incident on the upper substrate passes through the liquid crystal layer and is then reflected from the reflective film on the inner surface of the lower substrate. Then, the reflected light passes through the liquid crystal layer again to be emitted from the upper substrate, thereby contributing to display. On the other hand, in the transmissive mode, light emitted from a backlight to the lower substrate passes through the liquid crystal layer via the windows of the reflective film, and is then emitted from the upper substrate to the outside, thereby contributing to display. Therefore, in the region where the reflective film is formed, a portion thereof where the window is formed serves as a transmissive display region, and the other portion serves as a reflective display region.
However, this type of transflective liquid crystal display device has a problem in that a viewing angle is narrow in the transmissive display. The reason is that, since the transflective plate is provided on an inner surface of a liquid crystal cell to prevent the occurrence of parallax, reflective display should be performed by using only one polarizing plate provided on an observer side, which results in a low degree of flexibility in the optical design. Therefore, in order to solve this problem, the inventors, M. Jisaki et al., have proposed a liquid crystal display device using vertical-alignment-type liquid crystal, as disclosed in “Development of transflective LCD for high contrast and wide viewing angle by using homeotropic alignment,” M. Jisaki et al., Asia Display/ID W'01, pp. 133 to 136 (2001). The liquid crystal display device has the following three features:
(1) A ‘VA (vertical alignment) mode’ is used in which liquid crystal molecules having negative dielectric anisotropy are vertically aligned with respect to substrates in an initial state, and are then inclined when a voltage is applied;
(2) A ‘multi-gap structure’ is used in which the thickness (cell gap) of a liquid crystal layer in a transmissive display region is different from that in a reflective display region; and
(3) An ‘alignment dividing structure’ is used in which each transmissive display region is formed in the shape of a regular octagon, and a projection is provided at the center of the transmissive display region on a counter substrate to make the liquid crystal molecules incline in all directions in the transmissive display region.
In a transflective liquid crystal display device disclosed in Japanese Unexamined Patent Application Publication No. 11-242226, for example, a switching element is formed below a reflective film, and a contact hole reaching a pixel electrode is formed in a reflective display region. However, it is difficult to form both the switching element and the contact hole below the reflective film as the structure becomes more complicated, which results in a reduction in aperture ratio. In addition, the contact hole is formed by a photolithography technique. In this case, a tapered region may be formed in the vicinity of the contract hole due to side etching at the time of development or according to the accuracy of exposure. The tapered region causes alignment disorder of liquid crystal and low contrast. In particular, when liquid crystal is in a vertical alignment mode, the liquid crystal is randomly inclined due to the alignment disorder, and a discontinuous line, called disclination, appears at boundaries with other liquid crystal alignment regions, which causes, for example, residual images. In addition, since the liquid crystal alignment regions have different viewing angle characteristics, they appear as a spotted pattern when viewing the liquid crystal display device in an oblique direction.